Reverse osmosis water purification units for providing pure water for drinking and cooking are now in wide use. For home usage, these systems generally comprise a cold water source under pressure, a filter cartridge having a cold water inlet, a purified water outlet, and a brine outlet, a purified water storage tank, and a purified water faucet. The cartridge contains a semipermeable membrane for separating salts and other contaminants from the feed water.
Improvements in the design and manufacture of reverse osmosis cartridges permits the installation of a unit which produces several gallons per day of pure water, including a storage tank, in very small areas, e.g., under a kitchen sink. Most cartridges designed for home use employ a spiral-wound module where a purified water collection channel is formed between two sheets of membrane, all of which are wrapped around a perforated product water tube. Water flows through the membrane and into the water collection channel, eventually accumulating in the product water tube. The spiral-wound elements take the form of an elongated cylinder having a feed water inlet at one end, and purified water and contaminated water outlets at the other end. An example of such a cartridge is described in Bray, U.S. Pat. No. 3,504,796.
A difficulty which persists in residential reverse osmosis purification units is the tendency of the cartridge to become fouled on the feed water side of the membrane. The membrane may become clogged with small particulate matter, or an unduly high concentration of impurities which have been separated from the water may create scale and/or greatly reduce the efficiency of the separation process. While it is customary to have a very small, continuous flow of feed water through the apparatus, any flow greater than a few ounces per minute wastes a substantial amount of water and creates unnecessary expense. On the other hand, a very low flow (e.g., less than 3 ounces per minute) is insufficient to sweep the impurities away from the unit. Additionally, very low flows of impure water through restricted orifices tend to form deposits on the orifices, eventually restricting and shutting off the flow entirely.
One method of dealing with this problem has been to provide a hand-operated valve on the feed water line to the cartridge permitting a user to open the valve and flush the unit thoroughly with a high flow of feed water. Normally, depending on the quantity and types of impurities in the feed water, users are instructed to flush the cartridge for several minutes every day. Experience has shown, however, that while many users diligently follow instructions immediately subsequent to installation of a purification unit, after a short period of time daily flushing does not occur. Indeed, many users forget to flush the cartridge for months at a time, resulting in very poor purification performance.
Accordingly, it is an object of the invention to provide a reverse osmosis water purification system which will flush automatically without the user specifically intending to flush the system. It is another object of the invention to provide a water delivery system which will flush upon the occurrence of a user's opening a cold water faucet in a sink. It is yet another object of the invention to provide a reverse osmosis water purification system which will flush upon the actuation of a non-related electrical circuit. These and other objects of the invention are accomplished by the system of the invention, a preferred embodiment of which is set forth herein.